The first treatise on calendric astronomy was compiled C1300 B.C.and is known as “The Vedāṅga Jyautiṣa. It gives rules for framing calendar covering a five-year period, called a ‘Yuga’. In this yuga-period calendar, there were 1830 civil days, 60 solar months, 62 synodic lunar months, and 67 sidereal lunar months. The calendar was luni-solar, and the year started from the first day of the bright fortnight when the Sun returned to the Delphini star group. Corrections were made, as required, to maintain this stipulation to the extent possible. The Vedāṅga calendar was framed on the mean motions of the luminaries, the Sun and the Moon, and was based on approximate values of their periods. Vedāṅga Jyautiṣa calendar remained in use for a very long time from C 1300 B.C. to C 400 A.D. when Siddhānta Jyautiṣa calendar based on true positions of the Sun and the Moon came into use and gradually replaced totally the Vedāṅga calendar.